Polyolefine-polyacrylate based thermoplastic elastomer

ABSTRACT

A thermoplastic elastomer is achieved by absorbing an acrylate monomer, an initiator and eventually a diacrylate into polyolefin particles, after which the temperature is raised and the acrylate polymerises into the polyolefin and forms a dispersed phase, which has been functionalized by copolymerising a functional monomer together with the acrylate. As a compatibiliser a grafter polyolefin is used, which is melt-blended after the polymerisation into the thermoplastic elastomer or before the polymerisation into the polyolefin.

The invention concerns a polyolefine based thermoplastic elastomer whichcan be prepared without a separate vulcanisation stage and which hasbeen achieved by the polymerisation of acrylate into the polyolefinematrix. Especially the invention concerns such thermoplastic elastomersin which polyacrylate has been functionalised.

Thermoplastic elastomers are polymers which have the good processingproperties of thermoplastics but have the same physical properties asvulcanised rubbers. This combination of properties can be obtained sothat the material has both soft and elastic segments, with low glasstransition temperature t_(g), and a rigid eventually crystalline segmentwith a high glass transition temperature or a high melting point. Therigid and soft segments must be thermodynamically incompatible with eachother, so that they form separate phases. Thermoplastic elastomers donot need any separate vulcanising stage, in the contrary to conventionalrubber, and they can be processed to different articles with theprocessing methods normally used with thermoplastics, like extrusion,injection moulding and blow moulding. On the contrary to rubber,thermoplastic elastomers can also be reprocessed if necessary, forexample when recycling material from the processing stage.

Thermoplastic elastomers can be divided into two main groups, blockcopolymers and thermoplastic/elastomer blends. A well=known example ofblock copolymers which are thermoplastic elastomers is the anionicallypolymerised block copolymer of styrene and butadiene (SBS) and thehydrogenised form of the same (SEBS). Drawbacks of these polymers arepoor weather resistance, poor oil resistance and the high price.

An example of materials which belong to the other main group ofthermoplastic elastomers, are blends of polypropylene andethylene/propylene rubber or ethylene/propylene/diene rubber. They areusually made by blending the two main components and additives in anextruder. Because the continuous phase is polypropylene the material hasgood oil resistance properties.

Finnish patent application FI931863 describes a method to produce athermoplastic elastomer having a polyolefine as a continuous phase and apolyacrylate as a dispersed phase. The acrylate is polymerised into thepolyolefin. In the patent application FI946055 it has been noticed thateven better properties can be achieved and tailored by using a blend oftwo or more polyolefins, from which one is polar.

It has now, surprisingly, been observed that by copolymerising to theacrylate phase suitable functional monomers and by adding to thepolyolefine phase polyolefines grafted with functional groups, chemicalbonds or strong secondary effects can be achieved between the phases.Then also the physical and thermal properties of the elastomers areremarkably improved.

In the functional polyolefines, the functional monomers can beunsaturated carboxylic acids, their anhydrides or other carboxylic acidderivatives, like carboxylic acid esters. Typical examples of suchmonomers are maleic acid anhydride, acrylic and methacrylic acid andglycidyl(meth)acrylate. The amount of the functional monomer is 0.1-10%by weight, preferably 0.5-2% by weight, based on the amount ofpolyolefine. The functional polyolefine can be added either to thepolyolefine before the impregnation of acrylates or it can be blendedwith the elastomer after the polymerisation.

According to the invention, the polyacrylate phase can thus befunctionalised by adding to the acrylate monomer one or more functionalmonomers. The functional monomers can be of the same type which are usedin the grafting of polyolefine. Especially recommendable areα-unsaturated carboxylic acids, oxazolines and epoxy-, amino- andhydroxyfunctionalised (meth)acrylates, from which, as examples, can bementioned glycidylmethacrylate, 2-tertbutylaminoethylmethacrylate,propyleneglycolmonomethacrylate and monomethacryoloxyethylphthalate. Theamount of the functional monomer is 0.1-15% by weight, preferably0.5-10% by weight, of the amount of the rubber phase.

Also according to the invention, the polyolefine can be some polyolefineas such or a blend of two or more polyolefines. If more than onepolyolefine is used they are melt blended by using extrusion or othermelt blending equipment.

The elastomeric material according to this invention can be made by someknown method in which monomers are polymerised by free radicalpolymerisation technique into polyolefine matrix, e.g. by the Finnishpatent 88170. In principal the production is made so that the acrylatemonomer, the functional monomer and optionally diacrylate monomer, andthe initiatior is first absorbed into polyolefine particles. When allmonomers and the initiator have been absorbed, the temperature iselevated and the initiator decomposes and the acrylate and thefunctional monomer are polymerised. During the impregnation thepolyolefine particles swall to some extend, but maintain their particlestructure during both the impregnation and also the polymerisation.

The polyolefine matrix can thus be a homo- or copolymer of ethylene orpropylene or a blend of two or more polyolefines.

A comonomer for ethylene polymer can be vinyl acetate, vinyl chloride,propylene or some other α-olefin, C₁ -C₂ -alkylacrylate and-methacrylate, acrylic acid or methacrylic acid, hydroxyalkylacrylate or=methacrylate, glycidylacrylate or -methacrylate, dienes such ashexadiene-1,4, hexadiene-1,5, heptadiene-1,6, 2-methylpentadiene-1,4,octadiene-1,7, 6-methylheptadiene-1,5 and polyenes such as octatrieneand dicyclopentadiene. Also ethylene-α-olefin-polyene-terpolymeres canbe used. Useful α-olefins include propylene, butene, pentene, isoprene,hexene or their mixtures and useful polyenes include hexadiene-1,4,HEXADIENE-1,5, heptadiene-1,6, 2-methylpentadiene-1,4, octadiene-1,7,6-methylheptadiene-1,5, octatriene, dicyclopentadiene. In case that theethylene polymer is a copolymer, the share of ethylene must be at least50% by weight.

Propylene copolymers must consist over 50% by weight propylene and canbe random- or block copolymer of propylene and ethylene or also otherα-olefines can be used as comonomers, like dienes such as hexadiene-1,4,hexadiene-1,5, heptadiene-1,6, 2-methylpentadiene-1,4, octadiene-1,7,6-methylheptadiene-1,5 and polyenes such as octatriene anddicyclopentadiene.

If polyolefine blends are used, the components are melt blended in anextruder or another type of melt blending equipment before theimpregnation and polymerisation stages. Depending on the polarity of thecomponents in the polyolefine blend the impregnation of the acrylateamount occurs mostly into the more polar component. By the selection ofcomponents having different polarities the morphology and properties ofthe end products vary. It is preferable to choose the melt viscosity ofthe components so that the component which has the highest operatingtemperature simultaneously also has lower melt viscosity so that itbecomes the matrix in the polyolefine blend. In this way the operatingtemperature of the end product becomes also higher.

Suitable acrylate monomers are acrylates and methacrylates the polymersof which have low glass temperatures, i.e. they are rubberlike at theroom temperature and lower temperatures, preferably at the temperaturebelow -20° C. The glass temperature of the polyacrylate specifies thelower operating temperature of the material, below the glass temperaturethe polyacrylate is rigid and inelastic and the elastomeric propertiesof the material are lost. Suitable acrylates are alkylacrylates havingone or preferably two or more carbon atoms in the alkyl chain.Methacrylates having a glass temperature low enough arealkylmethacrylates having 4 or more or preferably 8 or more carbon atomsin the alkyl chain. These monomers can be used alone or in mixtures oftwo or more monomers. Together with the above mentioned monomers, alsosmaller amounts of monomers having less carbon atoms in the carbon chaincan be used. The glass temperature of the final product can thus betailored. According to this invention one or more above describedfunctional monomers are added to the acrylate monomer.

The end product can be tailored, if needed, according to the endapplication e.g. by adding oil to the acrylate or to the final polymerduring the processing. Oils can be the same that are normally used tosoften rubber, e.g. paraffinic, naphthenic, aromatic and synthetic oilsas well as plasticisers for thermoplastics such as e.g. dioctylphthalat.The amount of added oil can typically be 0-40% by weight in the finalproduct.

The properties of the end product like the rigidity and the operatingtemperature can be adjusted by the addition of conventional fillers liketalc, caolin, CaCO₃, silica. The amount of fillers is typically 0-70% byweight in the end product.

The amount of polyacrylate and polyolefine in the end product depends onmany factors, like the polyolefine type, the amount of possibly used oiland fillers and also on the usage of the end product. Typically, theratio between polyacrylate and polyolefine is 0.5-5, preferably 0.5-2.

The crosslinking of the product can be improved by adding already to thereactor some acrylate, which has two or more double bonds. During thepolymerisation these acrylates copolymerise to different acrylate chainsand the polyacrylate phase is crosslinking. The suitable amount of thecrosslinking agent is 0-15% by weight. Some acrylates crosslinkspontaneously without any addition of diacrylate. One of these isbutylacrylate.

Initiators which can be used to the polymerising of acrylate are thoseinitiators conventionally used in the free radical polymerisation ofvinyl monomers, being organic peroxides like e.g. benzoylperoxide,lauroylperoxide, t-butylperbenzoate, t-butyl-peroxy-2-ethylhexanate,t-butylperoxide, dicumylperoxide, di-t-butylperoxide,bis(t-butylperoxyisopropyl)benzene, t-butylperoxyisopropylcarbonate,2,5-dimethyl-2,5-di-t-butylperoxyhexane,2,5-dimethyl-2,5-di-(t-butylperoxy)hexyne-3, and azo compounds likeazobisisobutyronitrile and azobisdimethylvaleronitrile.

Also more than one initiator can be used so that the polymerisation isstarted with an initiator having a lower half temperature and is endedwith one having higher half temperature. The amount of the initiator is0.001-2% by weight, preferably 0.1-1% by weight, based on the monomeramount.

As it was already mentioned, the elastomer according to this inventioncan be made by some known method in which the monomer is polymerised bythe free radical method into the polyolefin matrix. The impregnation ofthe acrylate and the initiator can thus be made in the total absence ofwater, by adding some water, by adding water when more than half to heacrylate has been impregnated. These methods are in principal describedin the Finnish patents FI85496, FI86642 and FI88170. The impregnationcan also be made in the presence of the total amount of the suspensionwater as in the patent U.S. Pat. No. 4,412,938. The impregnation andpolymerisation can also be made simultaneously according to the Germanpatent publication DE 2.907.662 by keeping the water suspension of thepolyolefine at an elevated temperature and by adding slowly the acrylateand the initiator.

The polyolefine and polyacrylate type and amount affect the propertiesof the end product and the end product can be tailored with themaccording to this invention. The elastomer according to the inventionhas especially good mechanical properties compared to respondingelastomers in which no functional monomer is used among the acrylate andno functional polyolefine is used to improve the compatibility of thephases. Thus the elastomer according to the invention is especiallysuitable to products in which good mechanical properties are important,but is of course suitable to all applications in which conventionalrubber or thermoplastic elastomers are used. As examples can bementioned products for construction, car and electric industry and manytechnical products.

EXAMPLES 1-10

Polyolefine pellets and a monomer solution containing n-butylacrylate(nBA), functional monomer (FM) and a crosslinking agent(1,6-hexanedioldiacrylate, 1,6-HDDA) as well as an initiator(2,5-bis(t-butylperoxy)-2,5-dimethyl-3-hexyne) were added to thereactor. The function monomers used and their functional groups were thefollowing:

glycidylmethacrylate (GMA), epoxy group

2-t-butylaminoethylmethacrylate (TBAEMA), secondary amin group

polypropyleneglycolmonomethacrylate (PPGMMA), hydroxyl group

monomethacryloyloxyethylphthalate (MMAOEP), carboxy group

The reactor was rinsed with a nitrogen flow in order to remove oxygen.The reactor was closed and its temperature was raised to theimpregnation temperature and the monomer solution was absorbing into thepellets. Thereafter, the suspension water, heated to the impregnationtemperature, was added to the reactor as well as the suspension agentstricalsiumphosphate and sodiumdodecylbenzenesulphonate. After the wateraddition the temperature of the reactor was raised so much that theinitiator started to decompose and start the polymerisation. Thepolymerisation was continued for 5.5 hours by raising the reactortemperature gradually so that the final temperature was 132° C. Afterthe polymerisation the pellets were washed with a weak hydrochloric acidsolution, after which they were dried for after treatment. Thepolymerisation conditions for examples 1-10 are presented in Table 1. Inthe table there is also presented the gel content after thepolymerisation, which has been measured by extracting the specimen inboiling xylene for 20 hours. As an initiator in all polymerisations wasused 2,5-bis(t-butylperoxy)-2,5-dimethyl-3-hexyne, 0.2 mole-% from theamount of polypropylene. The total amount of monomer solution chargedinto the reactor was 90 mol-% from the amount of polypropylene. Thepolypropylene used in all polymerisations was a random polypropylene(2.5 mol-% ethylene) produced by Borealis Polymers Oy, tradename ZC2076DNA, melt index 20.

                                      TABLE 1                                     __________________________________________________________________________    Polymerisation conditions, Examples 1-10                                             FM content   Impreg.                                                                           Polym.                                                                              Mono-                                                                             Gel con-                                           in rubber  1,6-HDDA  tempe-  tempe- mer   tent after                     Ex   Functional           phase,     content,    rature,  rature,                                             yield, polym,                                 No   monomer           mol-%         mol-%      ° C. ° C.                                       mass-% mass-%                               __________________________________________________________________________    1 --   --     0,07  112 118-132                                                                             94  52                                            2     GMA      2       --    116    124-132    95     49                      3     GMA      5       --    116    124-132    95     50                      4     TBAEMA   2       0,07    114    122-132    94     42                    5     TBAEMA   5       0,07    115    125-132    92     36                    6     PPGMMA   2       0,07    116    126-132    96     44                    7     PPGMMA    5       0,07    121    124-132    91     43                   8     ROMM     2       0,07    119    125-132    89     46                    9     MMAOEP   2       0,07    119    124-132    96     51                    10     MMAOEP   5       0,07    123    124-132    92     53                 __________________________________________________________________________

The materials added during the melt processing after the polymerisationare given in Table 2. During the melt processing, bonds between thephases could be achieved by means of the reactions between thefunctional groups, which improved the mechanical properties of theblends. The amount functionalised polypropylene added was 5 mol-% of thetotal amount of the blend, PP-g-AA means a polypropylene grafted withacrylic acid, in which the amount of acrylic acid is 6.04 mol-%,PP-g-MAH means a polypropylene grafted with maleic acid anhydride, inwhich the amount of grafted maleic acid anhydride is 0.4 mol-%. The meltblending was made in a twin-screw extruder in which the die temperaturewas 180° C., processing time 2 min and speed 50 rpm.

                  TABLE 2                                                         ______________________________________                                        Functionalised polypropylene and zinc                                           acetate added during the ment blending                                        Ex.      Functional   Functionalised                                                                         Zinc acetate                                   no monomer (FM) polypropylene amount, mol-%                                 ______________________________________                                        1      --           --         --                                               2 GMA PP-g-AA --                                                              3 GMA PP-g-AA --                                                              4 TBAEMA PP-g-MAH --                                                          5 TBAEMA PP-g-MAH --                                                          6 PPGMMA PP-g-AA --                                                           7 PPGMMA PP-g-AA --                                                           8 ROMM PP-g-AA --                                                             9 MMAOEB PP-g-AA 0,7                                                          10 MMAOEB PP-g-AA 0,7                                                       ______________________________________                                    

Zinc acetate is added in the examples 9 and 10, because the bothfunctional monogroups are acid groups. The Zn²⁺ -group of zinc acetatecoordinates during the melt processing between the carboxylic group ofthe PP-g-AA in the polyolefine phase and the carboxylic group of theMMAOEP in the rubber phase, when acetic acid is liberated and a zinkbridge (R--COO--ZN²⁺ --OOC--R) is formed between the phases.

After the melt processing the material was pelletised and dried. Afterthat the materials were injection moulded at 180° C., the dietemperature being 30° C. From the material, it was made sheets (2×80×80mm), from which specimen for mechanical tests were punched. Themechanical and thermal properties of the blends are given in Table 3.

The mechanical properties were improved, compared with the comparativematerial (example 1), for all modified blends. The best results wereobtained with the blends 3 and 4,--in which the amounts of themodification agents in the rubber phase were: glycidyl methacrylate(GMA) 5 mol-% and 2-t-butylaminoethylmethacrylate (TMAEMA) 2 mol-%. Theproperties of the blend 4, modified with maleic anhydride graftedpolypropylene (PP-g-MAH) and TMAEMA were improved in average (mediate ofthe mould direction and the transverse direction); elastic modulus 30%,tensile, strength 13%, elongation 82% and tear strength (flow direction)47%. From these results it can be seen that the compatibilised blends towhich it was in the polymerisation stage added functional comonomer andin the melt processing stage functionalised polyolefin are clearlybetter compared to non-compatibilised blends.

Tensile strength, elongation at break and elastic modulus are made bythe standard method ISO 37, tear strength by the method ISO 34 (trousertest) and hardness by method ISO 868. Glass transition temperatures aremeasured by DMTA, heating speed 5°/min, three point bending method, 1Hz.

                  TABLE 3                                                         ______________________________________                                        The mechanical and thermal properties of the blends. Properties are given      in the table both in flow direction and in the transverse direction          (MD/TD)                                                                                        Elonga-            Hard-                                                                              T.sub.g                                   Tensile   tion at  Elastic Tear ness rubber T                                                                           .sub.g                           Ex   strength        break    modulus     strength          Shore                                                          phase  matrix                    No      MPa        %           MPa         kN/m           D   °                                                     C. ° C.                 ______________________________________                                        1   10,7/8,9 160/90  250/230                                                                              35    38   -45,3 -2,0                               2    12,3/10,4  80/70    305/330   52        40   -43,5   -2,7                3    12,2/10,5  205/100  330/305   47        40   -41,6   -2,0                4    12,1/10.0  180/235  340/275   52        40   -44,0   -1,9                5    11,8/10,1  205/225  325/290   40        40   -41,7   -1,2                6    11,3/9,6    200/170  290/265   38        39   -47,9   -2,3                                                           7    11,9/9,9    200/110                                                     320/300   36        40                                                        -48,4   -2,7                       8    12,6/10,8  120/255  355/345   38        42   -48,3   -2,9                9    11,8/10,3  140/220  300/275   36        41   -44,8   -4,9                10    12,2/10,3  165/175  255/225   32        40   -42,3   -2,5             ______________________________________                                    

EXAMPLES 11-22

In these examples, polyolefin blend was used instead of singlepolyolefin. Polyolefin components were blended in a corotatingtwin-screw extruder of type Werner & Pfleiderer (D=25 mm, L/D=39) usingmelt temperature 190° C., residence time on an average 2 min and a screwspeed 200 rpm. The extrudate was cooled in a water bath and waspelletised to 3 mm pellets. Thereafter the pellets were dried at 70° C.for 5 hours before the impregnation stage. The structure of the abovementioned blend has been photographed by an transmission electronmicroscope and it has been seen that the dispersed phase is a copolymerof ethylene and butylacrylate (EBA) and the continuous phase is acopolymer of propylene and ethylene. The diameter of the particles isabout 0.5-μm.

Polyolefine pellets containing polyolefine blend, acrylate, initiatorand possible 1,6-hexanedioldiacrylate were added to the reactor. Thereactor was filled and emptied three times with 7-8 bar nitrogen inorder to remove oxygen from the reactor. After that the temperature wasraised to the impregnation temperature and kept there, stirringcontinuously, until the major part of the acrylate and the initiatorswere impregnated. The impregnation time was 1-3 hours depending on thepolyolefine quality. Thereafter, the suspension water, also rinsed withnitrogen, was added. The suspension water contained tricalsiumphosphateand sodiumdodecylbenzenesulphonate as a suspension agent. Thetemperature of the suspension water was the same as the impregnationtemperature. After the water addition the temperature was raised so muchthat the initiator started to decompose and initiate the polymerisation.The polymerisation took 7-12 hours depending on the components in thepolyolefine blend. The polymerisation product was washed and dried afterthe polymerisation. Several different materials were made according tothis model, see Table 1, examples 1-12. The structure has beenphotographed by a transmission electron microscope. The dark dispersedphase is EBA and the dispersed phase in EBA is polybutylacrylate. Thecontinuous phase is a copolymer of propylene and ethylene. The diameterof the polyacrylate particles is about 0.1 μm.

The polymer materials made according to Table 4 were injection mouldedto sheets having the size of 80×80 mm and the thickness of 2 mm, at 200°C. The necessary test bars were punched from the sheets. The mechanicalproperties are in Table 5. Elongation at break and tensile strength havebeen measured from test rods which are punched transverse to the flowdirection of the injection moulding.

All need polyolefine qualities are commercial products of BorealisPolymers Oy:

EBA1=NCPE 6417, ethylene/butylacrylate copolymer (17% butylacrylate,melt index 7)

EBA2=NCPE 6420, ethylene/butylacrylate copolymer (17% butylacrylate,melt index 1,5)

EBA3=NCPE 6427, ethylene/butylacrylate copolymer (27% butylacrylate,melt index 4)

PP1=XC20 76DNA, polypropylene (random copolymer, melt index 20)

PP2=VC50 76DNA, polypropylene (homopolypropylene, melt index 50)

                                      TABLE 4                                     __________________________________________________________________________    Polymerisation conditions of the blends, Examples 11-22.                                    Acry-                                                                             Diac-                                                         Ex.           PO blend late   rylate                                                                           .sup.3 Initiator Impreg. Polym.                                               Gel.sup.1                                    Nr    PO-blend         w-%       w-%       w-% w-% type.sup.2  °                                        C. ° C. %                           __________________________________________________________________________    11                                                                              EBA1/PP1                                                                            30/70                                                                            30 70  1,5 BPIC 84  85-115                                                                            75                                           12 EBA2/PP1 50/50 60 40 0,3 BPIC  67 85-115 51                                13 EBA2/PP1 50/50 50 50 0,3 BPIC  84 85-115 63                                14 EBA2/PP1 50/50 45 55 0,3 BPIC  88 90-115 59                                15 EBA2/PP1 50/50 50 50 0,3 BPIC  87 90-120 55                                16 EBA2/PP1 60/40 50 50 0,3 BPIC  86 88-120 56                                17 EBA2/PP2 70/30 60 40 0,3 t-BPB 78 80-130 51                                18 EBA2/PP2 65/35 60 40 0,3 BPIC  78 85-120 56                                19 EBA3/PP1 60/40 60 40 0,3 BPIC  58 70-120 45                                20 EBA3/PP1 60/40 60 40 0,3 BPO   56 60-100 54                                21 EBA3/PP1 55/45 60 40 0,3 BPO   56 60-100 51                                22 EBA2/PP2 70/30 60 40 0,3 BPIC  77 80-120 47                              __________________________________________________________________________     1) Gel contend measured in boiling xylene during 16 hours.                    2) BPO = benzoylperoxide, BPIC = tertbutylperoxyisopropylcarbonate, tBPB      tertbutylperoxybenzoate                                                       3) Diacrylate = 1,6hexanedioldiacrylate                                  

                  TABLE 5                                                         ______________________________________                                        Mechanical properties of the materials in the examples 11-22.                           Tension  Elongati              Tear                                       strength.sup.2 on at                      Compres-      strength.sup                                             .5                                     Exp   MPa,          break.sup.1 %, IRHD.sup.3 sion set.sup.4   kN/m                                                   Nr    MD/TD         MD/TD                                                         normal    %                                                              MD/TD                                ______________________________________                                        11    5,8/4,9  45/80     86     25     4/5                                      12 10,5/9,7  180/300 96 25   19/27                                            13 8,6/6,8  100/210 93 37   20/21                                             14 8,5/7,0  120/210 90 -- 11/14                                               15 8,0/7,0  110/240 93 25   13/19                                             16 9,0/8,5  100/220 89 30   14/14                                             17 9,0/8,0  140/220 92 31   15/19                                             18 9,0/7,0  110/260 94 -- 13/20                                               19 9,0/8,0  110/190 92 -- 11/14                                               20 9,0/9,0  110/260 92 36   15/19                                             21 9,0/8,0  130/300 93 38   15/22                                             22 9,0/8,0  110/220 93 29   12/19                                           ______________________________________                                         1) Elongation at break measured by ISO 37                                     2) Tensile strength measured by ISO 37                                        3) Hardness, IRHD, measured by ISO 48                                         4) Compression set after 24 hours at room temperature by ISO 815              5) Tear strength measured by ISO 34                                           MD = measured in the flow direction of the material in injection moulding     TD = measured against the flow direction in the injection moulding       

The amount of polyacrylate has the biggest effect to the hardness of theproduct, the higher amount of polyacrylate the softer product, compareexamples 12, 13 and 14.

EXAMPLES 23-25

In table 6 is presented the polymerisation conditions for the blends ofexamples 23-25. There example 23 only contains a polyolefine blend andpolyacrylate while the blend of example 24 contain 10% of weightnaphthenic oil, Nypar 840. The blend in example 25 contains additionally20% of weight calcium carbonate.

                  TABLE 6                                                         ______________________________________                                        Polymerisation conditions of blends, Examples 23-25.                                                      Imp-       Filler                                                                              Oil content                        Ex.          PO     blend  reg.      Polym.    w-%    w-%                     Nr  PO-blend w-% w-% ° C. ° C. CaCO.sub.3 Nytex 840           ______________________________________                                        23  EBA2/PP1 50/50  50    85   85-120                                                                              --    --                                   24 EBA2/PP1 50/50 50 85 85-120 -- 10                                          25 EBA2/PP1 50/50 50 85 85-120 20   10                                      ______________________________________                                    

Diacrylate=1,6-hexanedioldiacrylate, 0.3% by weight, in all examples13-15 Initiator BPIC

The mechanical properties of examples 23-25 are given in Table 7. Theoil and calcium carbonate addition decreased the tensile strength, butthe elongation at break increases. Also the material becomes softer,from 93 to 88 IRHD normal by oil and filler addition. The compressionset becomes about 20% as a result of the oil addition.

                  TABLE 7                                                         ______________________________________                                        Mechanical properties of the materials of examples 23-25                                  Tensile  Elonga-                                                        strength.sup.2 tion at                    Compres-                        Exp MPa,          break.sup.1 %, IRHD.sup.3 sion set.sup.4                    Nr  MD/TD         MD/TD            normal    %                              ______________________________________                                        23      9,0/9,0  140/290     93    35                                           24 7,0/7,0 160/160 89 89                                                      25 6,0/6,0 170/300 88 28                                                    ______________________________________                                         1) Elongation at break measured by ISO 37                                     2) Tensile strength measured by ISO 37                                        3) Hardness, IRHD, measured by ISO 48                                         4) Compression set after 24 hours at room temperature by ISO 815              MD = measured in the flow direction of the material in injection moulding     TD = measured against the flow direction in the injection moulding       

A comparison between an purely PP-based material (=REF) and PP/EBA-blendbased material (example 13) has been made in table 8. The referencematerial contains only PP1 (see table 4) as a polyolefine while thepolyolefine in the material in example 13 is a blend of PP1 and EBA2.The hardness of both materials is about the same (91 and respectively 93IRHD normal), which makes it possible to directly compare the materials.The tear strength in the polyolefine blend (PP/EBA) based material isabout 10 times better than the tear strength of the reference material.A clear increase can also be seen in the tensile strength.

                  TABLE 8                                                         ______________________________________                                        Comparison between purely PP-based (REF) and PP/EBA-based TPE                   (example 13)                                                                                  REF       Example 13                                        ______________________________________                                        Polyolefine blend, PP, w-%                                                                      PP1, 100% PP1, 50%                                            Polyolefine blend, EBA, w-%    --          EBA2, 50%                          Polyolefine (blend or PP)         33% (PP1)     50% PP1 + EBA2                Acrylate, w-%                  67%           50%                              Diacrylate (1,6 hexanedioldiacry- 3%            0,3%                          late), w-%                                                                    Initiator type                    Trig. 145     BPIC                          Impregnation temperature          120° C. 84° C.                Polymerisation temperature        130-150° C. 85-115° C.                                   Gel                               63%                                           63%                                              Tension strength, MPa, MD/TD      6,9/6,6       8,6/6,8                       Elongation at break, %, MD/TD     45/56         100/210                       IRHD normal                       91            93                            Tear strength, kN/m, MD/TD        2,8/3,4       19,8/20,5                   ______________________________________                                    

We claim:
 1. A thermoplastic elastomer produced by the process whichcomprises:a) combining polyolefin particles, at least one acrylatemonomer and a free radical polymerization initiator, wherein said atleast one acrylate monomer includes a functional acrylate monomer; andb) heating the resultant mixture to cause said acrylate to polymeriseand impregnate into said polyolefin particles and to cause crosslinkingof said acrylate to produce a polyolefin-polyacrylate blend, whereincrosslinked polyacrylate comprises a dispersed phase in a continuousphase of said polyolefin.
 2. A thermoplastic elastomer according toclaim 1, wherein a functional polyolefin is combined with saidpolyolefin particle, said at least one acrylate monomer and saidinitiator.
 3. A thermoplastic elastomer according to claim 1, wherein afunctional polyolefin is blended with said polyolefin-polyacrylate blendafter said polymerisation.
 4. A thermoplastic elastomer, according toany one of claims 1-3, wherein said polyolefin particles comprise ablend of two or more polyolefines which have been melt blended.
 5. Athermoplastic elastomer, according to any one of claims 1-3, whereinsaid functional acrylate monomer is carboxylic acid, oxazoline, epoxy-,amino- or hydroxyfunctional (meth)acrylate.
 6. A thermoplasticelastomer, according to any one of claims 1-3, wherein the amount of thefunctional acrylate monomer is 0.1-15% by weight based on the amount ofthe acrylate monomer.
 7. A thermoplastic elastomer, according to claim 2or 3, wherein said functional polyolefine is carboxylic acid oranhydride or some other carboxylic acid derivative.
 8. A thermoplasticelastomer, according to claim 5, wherein the amount of the functionalpolyolefine in the elastomer is 0.1-15% by weight.
 9. A thermoplasticelastomer, according to claim 1, wherein the polyacrylate can becrosslinked by copolymerising the acrylate with a diacrylate or amultifunctional acrylate during the polymerisation or the acrylatecrossslinks spontaneously.
 10. A thermoplastic elastomer, according toclaim 1, wherein the polyacrylate has a glass transition temperaturelower than room temperature.
 11. A thermoplastic elastomer, according toclaim 1, wherein the monomers for the polyacrylate are alkyacrylateswith 2 or more carbon atoms in the alkyl chain, alkymethacrylates with 4or more or preferably with 8 or more carbon atoms in the alkyl chain,alkylacrylates and methacrylates which contain polar groups.
 12. Athermoplastic elastomer, according to claim 1, wherein the polyolefineis polypropylene, polypropylene containing comonomers, polyethylene orpolyethylene containing comonomers or a blend of them.
 13. Athermoplastic elastomer, according to claim 1, wherein the weightproportion between the polyolefine and the polyacrylate in the blend is0.1-5.
 14. A thermoplastic elastomer, according to claim 1, wherein upto 40% by weight oil is added into the polymerisation or during aseparate extrusion stage in order to make the material softer.
 15. Athermoplastic elastomer, according to claim 1, wherein the end productcontains up to 70% by weight fillers.
 16. A thermoplastic elastomer,according to claim 1, wherein the elastomer is processed by conventionalprocessing methods like extrusion, injection moulding, blow moulding andcoextrusion with polyolefines.
 17. A thermoplastic elastomer, accordingto claim 1, wherein it has good oil and weather resistance properties.